Terminal Bronchioles
The respiratory airways can be divided into conducting and respiratory zones. The conducting zone comprises the nose, larynx, pharynx, trachea and structures like bronchi and bronchioles. In that, the terminal bronchioles form the distal part of the conducting zone. The terminal bronchioles are made of ciliated cuboidal epithelium that has non-ciliated club cells. These club cells secrete non-sticky proteins that help to maintain air passage in the smallest bronchioles. Also, they aid the bronchioles during the inspiration and expiration process.
Each terminal bronchiole further divides into respiratory bronchioles.
Respiratory Bronchioles
The respiratory zone consists of the respiratory bronchioles, alveoli and alveolar ducts. It is the main site for the exchange of O2 and CO2 with the blood. The alveolar ducts and the respiratory bronchioles are together responsible for around 10% of gas exchange. The remaining 90% is taken care of by the alveoli.
The bronchi divide the number of times before forming the respiratory bronchioles. Thus, they are the narrowest air tracts. The respiratory bronchioles are made of non-ciliated club cells and ciliated columnar epithelial cells. These bronchioles have side branches called alveolar ducts.
Difference between Terminal and Respiratory Bronchioles
Terminal Bronchioles |
Respiratory Bronchioles |
|---|---|
| They form the distal part in the conducting zone of the respiratory airways. | They form the initial portion in the respiratory zone of the respiratory airways. |
| The terminal bronchioles divide to make respiratory bronchioles. | The respiratory bronchioles side branch to form alveolar ducts. |
| They do not bear any alveoli. | They have alveoli. |
| The cells lining its lumen are made of ciliated cuboidal epithelium and non-ciliated club cells. | The cells lining its lumen are made of ciliated columnar epithelium and non-ciliated club cells. |
| They help in the conduction of gases in and out of the lungs. | They help in the exchange of gases at the lung surface. |
Explore: Human Respiratory System
Frequently Asked Questions
What is a bronchus?
The bronchus is a respiratory passage that helps in the conduction of gases into the lungs. The trachea branches into the right bronchus and the left bronchus. The gas exchange does not take place in the bronchi.
What are bronchioles?
The bronchus divides into small branches called the bronchioles. The bronchioles divide into smaller terminal bronchioles, which further divide into the narrowest respiratory bronchioles.
What are alveoli?
The alveoli are cup-shaped air spaces in the lungs that help in the exchange of O2 and CO2. They make up approximately 90% of the lung volume. The alveoli are seen as scattered-out pockets in the respiratory bronchioles. Then, they increase in number and line the alveolar ducts. Each alveolar duct opens into alveolar sacs, which have numerous clusters of alveoli.
Also Read: Gases-Exchange and Regulation
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